In the past decade, many tumor-associated peptides that serve as T cell antigens (in the context of MHC proteins) have been identified. Based on these findings, and recent insights into other aspects of T cell biology, there continues to be considerable effort on the development of T cell-based therapies of cancer. As is now apparent with monoclonal-antibody therapies, success with these T cell strategies will require diagnostic assays that determine whether a patient's cancer is antigen-positive (i.e. expresses the tumor pep/MHC on its surface). In this proposal, two investigators who have complementary expertise in T cell receptor (TCR) engineering (David Kranz) and in T cell-directed therapies of cancer (Phil Greenberg) will collaborate on the development of TCR-based assays for cancer diagnosis. We have recently shown that it is possible to engineer high-affinity TCRs that are specific for pepMHC molecules. Soluble forms of these TCRs can serve as novel probes to identify and quantitate the amount of a tumor antigen peptide presented on the surface of a tumor cell, in the context of an MHC class I molecule. TCRs against one of these tumor antigens, peptide WT1 from the oncogenic Wilm's tumor protein, will be explored in the present study. The goals of this proposal are to: Aim 1. Develop sensitive T cell receptor-based assays for detection of specific peptide-MHC on tumor cells, using an already available high-affinity TCR (m67a) specific for the pep/MHC complex SIYR/Kb. Aim 2. Engineer high-affinity TCRs against mouse WT1/Dh complexes, an animal model that will be critical for the development of optimal therapeutics and diagnostics against WT1 in humans. Aim 3. Engineer high-affinity TCRs against human WT1/HLA-A2 complexes, the antigenic complex known be expressed endogenously by various A2+ human tumors, including many leukemias. These TCR reagents should not only be useful for distinguishing tumor cells from normal cells, based on detecting the expression of a tumor antigen, but they should also identify patients with tumors that might be most susceptible to immunotherapeutic intervention.